FROGS AND THEIR RELATIVES 105 



I. (Optional.) Sketch of the mouth cavity. 



1. Open wide the mouth of a large frog and make a sketch to 



show the shape of the mouth cavity twice the natu- 

 ral size, and the shape and thickness of the upper 

 and lower jaws. 



2. Draw the following parts to show their location, size, and 



shape: jaw teeth, palate teeth, tongue, glottis, 

 nostril openings, swellings caused by the eyes. 



3. Farthest back in the throat find an opening that extends 



crosswise. It is the opening into the gullet, and is 

 just behind the glottis. Push the handle of the 

 forceps into this opening and draw it (in your 

 sketch) partly opened. 



4. Label upper jaw, lower jaw, jaw teeth, palate teeth, tongue, 



glottis, opening of gullet, nostril openings, swellings 

 caused by eyes. 



/. Structure of arms and leg 



Place a frog in a glass jar at least half full 

 of water to cause the animal to extend the hind 

 legs. 



1. Make a sketch (natural size) of an arm to show the 



shape and size of the following parts : upper 

 arm, elbow, forearm, hand, number of fingers. 

 Label each part. 



2. Draw one of the legs (natural size) to show the follow- 



ing parts : thigh (next the body), knee, shank, 

 ankle (elongated region above foot), foot, toes, 

 web between toes. Label each part. 



K. How a frog swims. 



Place an active frog in a sink or other 

 receptacle large enough to afford it room 

 to swim. The water should be deep enough 

 so that the frog will not strike the bottom with 

 the legs. Get the frog to swim the full length of 



